An integrative method to quantify contaminant fluxes in the groundwater of urban areas

Background, Aims, and Scope  Groundwater in urban areas is often contaminated and emission sources can be located close to groundwater wells. The delineation of contaminant plumes is difficult because of the various potential emission sources. Thus, detection, quantification and remediation of contaminated sites in a city need more integrative approaches. Methods  A method has been developed which allows quantification of mass fluxes of contaminants in groundwater between control planes. Budget zones along the flow path are defined to calculate a contaminant balance and to quantitatively reveal input areas. Concentrations and water budgets are used to calculate mass balances for each contaminant. The city of Darmstadt (Germany) was chosen to evaluate the method. Results  The groundwater monitoring wells (GMWs) upstream of the city showed anthropogenically superposed background values for all naturally occurring inorganic species. The contaminant concentrations increased in the city (probably influenced by road traffic, gas stations, leaking sewers, etc.). Downstream from the city, concentrations usually decreased. Organic compounds typical for urban environments, such as polycyclic aromatic hydrocarbons (PAH), locally exceeded drinking water regulations. In GMWs with high concentrations of organic contaminants in the city or downstream from industrial areas, a significant increase in Fe²⁺ and Mn²⁺ could be observed, in some cases coinciding with a decrease in NO₃, SO₄ and an increase in NH₄. Discussion  For typical urban contaminants, a positive budget was calculated in several zones, which shows that emissions from urban sources are reaching the groundwater. Negative budgets can be mainly explained with diving plumes and degradation. The input calculated from the individual budget zones is usually higher than the input estimated from urban emissions. Differences between the calculated and the estimated input can be explained with additional sources or (bio)degradation processes. Conclusions  It was confirmed that high concentrations of contaminants do not necessarily correlate with high fluxes. Integrative approaches can reveal areas of high contaminant mass input. The results obtained with the new method are plausible compared to the land use and the estimated urban input. The concentration pattern of Fe²⁺, Mn²⁺, SO₄ and NO₃ is partly due to natural processes, triggered by the degradation of organic matter and organic contaminants. Recommendations  Since this method includes mass balances and flux calculations, avoiding an overestimation of single point contaminant concentration, it is recommended to use this approach to quantify groundwater contamination in cities. Further research is focusing on the role of urban soils as natural reservoirs for the input of contaminants.     

Deep infiltration through a sandy alluvial fan in semiarid Niger inferred from electrical conductivity survey,vadose zone chemistry and hydrological modelling

In semiarid southwestern Niger, most of the groundwater recharge is indirect and occurs through endoreic ponds. Elsewhere in the landscape, there is no evidence of deep infiltration, with a possible exception for gullies and alluvial fans on sandy slopes. In order to verify this hypothesis, a detailed geophysical and geochemical survey was conducted on a large, representative mid-slope fan (6 ha). At this site, distributed hydrological modelling conducted over the encompassing endoreic catchment (190 ha) showed high losses of runoff water by infiltration. Electromagnetic mapping and 2-D electrical imaging survey were used to investigate the 35 m deep vadose zone; in addition, 8 boreholes were drilled following the geophysical survey to constrain the interpretation. Variations in apparent electrical conductivity measured in boreholes appear to be mainly linked with changes in the soil solution mineralization. An extrapolation throughout the area shows that apparent electrical conductivity of the ground is systematically lower below channels; this suggests localised leaching through the unsaturated zone. A physically-based, 2-D distributed hydrologic model was used to estimate the amount of surface water loss by infiltration for the 1992–2002 period. Depending on year, infiltrated volumes range from 1000 to 24 000 m³. This represents between 5% and 16% of the runoff that reaches the final outlet of the basin, an endoreic valley bottom pond where recharge to the aquifer has been shown to occur. Because leaching of the vadose zone is observed down to a depth of 10 m below channels, episodic groundwater recharge through sandy mid-slope fans is highly probable during rainy years.     

Augmenting freshwater availability in mountain headwater streams: Assessing the sustainability under baseline and future climate change scenarios

Mountain headwater streams are important freshwater sources, but they are mostly intermittent and highly susceptible to climate change. This paper examines the sustainability of augmented freshwater availability in mountain headwater streams for water supply under baseline and future climate change scenarios using an integrated modeling approach. The climate change data in the 2040s (2030–2059), under Representative Concentration Pathway 4.5 and 8.5 scenarios, were downscaled for the impact assessment. In the region, climate change raises the average precipitation by 5–7% and the temperature by 13–15% in the 2040s. SWAT–MODFLOW model, integrating Soil and Water Assessment Tool (SWAT2012) and finite-difference Modular Groundwater Flow (MODFLOW) models in a single package, was used to assess the water balance. Results show that extracting a minimum of 16.2 m³/day from the sand storage and 30 m³/day from the aquifer was possible without affecting the groundwater table and water yield. The average annual catchment recharge was 6% of the precipitation under the baseline simulation. Climate change is projected to reduce the average water yield and groundwater recharge by 26% and 19%, respectively. However, the water supply-demand is significantly small compared to the exploitable rate of water in the area. This study was based on limited data, and therefore the findings need to be interpreted with caution, though the model output was validated using satellite products. Construction of a series of sand dams is suggested to maximize the benefit under the potential climate change and water supply-demand increase.     

近60年鄯善县地下水补排量演变与坎儿井流量衰减关系

为揭示干旱区地下水补排量演变规律及其与坎儿井流量衰减的关系,通过梳理1949年以来鄯善县水资源开发利用、地下水资源调查评价资料,分析了地下水补排量的变化,划分地下水补排量演化的阶段。利用双变量相关分析法,分析了地下水主要补排量演化与坎儿井流量衰减之间的关系,并分析了其原因。结果表明：1）鄯善县地下水补排量的变化主要受人类活动影响,气候变化的影响微弱,且主要补排量变化的突变点与国家实施改革开放、西部大开发等政策的起始点相一致,政策是人为因素中的关键因素;2）坎儿井出流量与河道渗漏补给量、渠道渗漏补给量、田间入渗补给量、机井地下水开采量之间的相关系数依次为0.312、?0.327、?0.574、?0.959,说明坎儿井流量的衰减主要受机井开采地下水影响,其次为田间入渗补给量,河道和渠道（干支渠）渗漏补给影响较小;3）坎儿井出流量与地下水补排量的响应关系主要由其空间分布位置决定。该研究对坎儿井保护和超采区治理提供参考。     

采用氯离子示踪法计算沙漠降雨入渗量

为了研究巴丹吉林沙漠东南部地区的降雨入渗补给量,基于沙漠东南部两个剖面的氯离子质量浓度、质量含水率数据,利用氯离子示踪法计算了巴丹吉林沙漠东南部地区的降雨入渗补给量。结果表明乌海子、诺尔图地区的年平均补给率分别为0.81 mm/a和1.24 mm/a,仅占多年平均降雨量的0.9%和1.4%,因此当地现代降水对巴丹吉林沙漠东南部地区地下水的补给十分微弱,即当地现代降雨并非为此区域地下水的主要补给源。     

Indicators for assessing anthropogenic impact on urban surface and groundwater

Background, Aim and Scope  Our study focuses on the indication of anthropogenic impacts on the urban surface and groundwater in large cities, demonstrated for the cities of Halle/Saale and Leipzig (Germany). For the study we selected indicator substances such as xenobiotics, trace elements, and stable isotopes which are connected to human activities in urban areas. The xenobiotics reported here are the pharmaceutical carbamacepine, the polycylic musk compounds galaxolide and tonalide, the life style product caffeine, and industrial chemicals such as bisphenol A and t-nonylphenol. The investigated xenobiotics pose largely unknown risks to human health and the aquatic ecosystem. Trace elements are represented by the rare earth element gadolinium (Gd), used as magnetic resonance imaging contrast substance. Nitrogen isotopes in dissolved nitrate characterize the origin of nitrogen compounds, mixing and reaction processes. Methodology  River water was sampled along the flow path of the rivers Saale and Weisse Elster through the city of Halle/Saale, the rivers Luppe and Weisse Elster through the city of Leipzig. Separate samples were collected from the effluent of the local waste water treatment plants. Groundwater from Quaternary plain aquifers along the rivers and from different urban locations was collected at the same time. The indicators were analysed and assessed according to their sources, concentration and distribution patterns. Results and Discussion  Based on the nitrogen isotopic signature, dissolved nitrate in river water of the Saale was referred mainly to two sources: the effluent of the water treatment plant and a mixture of diffusive inputs from rain water channels, sewage leakages and agriculture activities along the rivers. The Gd anomaly was recognized in surface water of both cities, particularly in the effluent of the water treatment plants, but clearly attenuated in groundwater. We measured concentrations of xenobiotics in river and sewer water between 10 and 60,000 ng L⁻¹, and, in groundwater, one order of magnitude lower. Distinctions of xenobiotic patterns were found in river water before and after the effluent of treated waste water into the rivers. Degradation of endocrine disrupters and fragrances, but also persistence of carbamacepine were recognized as essential processes during waste water treatment. At the study site Halle/Saale, mass balances were set up for xenobiotics and water fluxes. Conclusions  At both sites, we demonstrated that indicators such as xenobiotics, gadolinium, and nitrogen isotopes are suitable for assessing anthropogenic impacts on urban water. However, the behaviour of these indicators in surface and groundwater has to be considered according to the different geochemical environments.     

三江平原井灌区地下水人工回灌量测算

针对近些年来三江平原大面积发展井灌水稻所导致的地下水位持续下降问题,以853农场为例,采用水量均衡法,测算了853农场2006—2009年维持地下水收支平衡及地下水恢复至适宜埋深条件下的人工回灌量,结果表明:维持地下水收支平衡所需回灌量均小于5 000万m3;地下水恢复至适宜埋深所需回灌量均为2亿m3左右,远远超过维持地下水收支平衡所需回灌量;若继续沿用现状地下水利用模式,未来所需回灌量会更大,建议当地加大地下水资源管理力度。研究成果为853农场乃至整个三江平原地下水资源恢复及可持续利用提供了科学依据。     

Structure and functioning of earthworm communities in woodland flooding systems used for drinking water production

Earthworms are known to influence water infiltration in soils, but most of the existing knowledge relates to grasslands and arable systems; little is known on the role of earthworms for water infiltration in forests. We studied earthworm populations and water infiltration rates in woodland flooding sites used for groundwater recharge and the production of drinking water. Intensive flooding may detrimentally affect earthworm populations and simultaneously result in clogging of the topsoil, with the latter being a common problem in groundwater recharge systems. However, clogging does not occur at our study site, the “Lange Erlen” (Basel, Switzerland) and total earthworm numbers and biomass in flooded sites exceeded those of non-flooded sites (+51% and +71%, respectively). Total earthworm numbers (r = 0.85***), numbers of endogeic (r = 0.64*) and epigeic (r = 0.81**) earthworms and numbers of two species (Lumbricus rubellus, r = 0.62* and Allolobophora chlorotica, r = 0.77**) significantly correlated with water infiltration rates. The results suggest that short-term flooding (max. 10 days) interrupted by longer recovery periods favor earthworm populations which likely contribute to the long-term (ca. 100 years) sustainability of the studied forest groundwater recharge system and thereby to effective and cost efficient drinking water production.     

Development and practical test of a weighable groundwater lysimeter for floodplain sites

Presently, the soil water balance of flood‐influenced soils in fluvial plains is insufficiently described. The new development of a weighable groundwater lysimeter is the basis for recording the water‐balance components precipitation, evapotranspiration, groundwater recharge, capillary rise, and interaction with the water course. Soil‐hydrologic measuring setups at two floodplain sites of the Elbe river serve for direct comparability of lysimeter measurements with data obtained on site. A groundwater control was designed for lysimeters that automatically adjusts the current groundwater level at the floodplain measuring setups and quantifies inflow into or outflow from the lysimeter. It turned out that the lysimeter developed is capable of identifying the individual water‐balance quantities at high accuracy. Contrary to previous assumptions, it was possible to prove groundwater recharge for the floodplain sites.     

黄土高原粗质地土壤剖面水分运动与浅层地下水补给可能性模拟

黄土高原水土流失严重,生态环境脆弱,水资源短缺,地下水对保障区域社会经济发展和维持生态系统平衡具有重要意义,而该区的地下水转化和补给机制尚不明确。为探究黄土高原水蚀风蚀交错区土壤剖面深层水分运动及降水对浅层地下水补给的可能性,利用六道沟小流域分布的粗质地风沙土样地2013—2016年土壤剖面0~600 cm含水量数据,运用HYDRUS-1D模型对各土层水力参数进行反演和验证,并用于模拟样地土壤深剖面0~1 500 cm水分运移过程。结果显示,在平水年2014年(439 mm)和干旱年2015年(371 mm),0~600 cm土壤含水量生长季末与生长季初持平或略有亏缺;降水充沛年2013年(669 mm)和2016年(704 mm)土壤含水量生长季末远高于生长季初,降水入渗深度超过观测深度(600 cm)。深剖面水分运动模拟显示,2014年和2015年剖面含水量变化不明显,水分向深层运移微弱缓慢;但是,2013年和2016年降水可分别入渗运移至1 100 cm和1 200 cm深度,远超过样地上生长的旱柳根系区域,可能补给浅层地下水。在4年模拟期间,平均土壤蒸发为14.87 cm·a-1,平均植物蒸腾为33.70 cm·a-1,土壤水分主要以植物蒸腾形式损耗。在2个丰水年,得益于较充足的降水和粗质地风沙土壤的高入渗率,降水大量转化为土壤水快速向下入渗运移,模拟显示当年生长季末降水最深运移至1 200 cm,至年末已超过模拟深度(1 500 cm),水分继续运移可能补给浅层地下水。相关研究结果为黄土高原水蚀风蚀交错区地下水来源和补给机制提供理论依据。     

多因素影响下土壤上升毛管水运动特性HYDRUS模拟及验证

基于饱和—非饱和土壤水分运动理论,通过HYDRUS-1D软件对多因素作用下的土壤上升毛管水运动进行模拟,研究土壤容重、黏粒含量、初始含水率、地下水埋深和时间5个因素对上升毛管水运动特性的影响。分别建立上升毛管水补给量和毛管水上升高度与各影响因素之间经验模型,其均方根误差均为0.003 cm,相关系数均大于0.99,决定系数均大于0.98(P0.01),计算值与实测值相对误差均小于11.25%。各影响因素对上升毛管水补给量的影响程度由大到小依次为时间、土壤容重、初始含水率、黏粒含量、地下水埋深,对毛管水上升高度的影响程度由大到小依次为时间、初始含水率、黏粒含量、土壤容重、地下水埋深。采用截距为0的线性函数对毛管水上升高度与上升毛管水补给量之间的关系曲线进行拟合,其决定系数均在0.96以上,表明其两者之间呈显著线性关系。该研究成果可为制定灌溉和排水以及盐碱地改良等措施提供理论依据。     

雨水回灌对深层承压含水层水质影响的模拟研究

[目的]揭示雨水回灌中污染物在深层承压含水层中的迁移扩散规律。[方法]以常规指标氯化物(Cl-)为研究对象,针对天津市市区第Ⅳ承压含水组,应用地下水模拟软件(groundwater modeling system,GMS)中的MODFLOW和MT3DMS模块分别进行地下水流场和溶质迁移模拟。模拟了4种不同的Cl-质量浓度和水量条件对溶质运移的影响。[结果]当溶质质量浓度相同时,回灌水量增大4倍,等Cl-浓度面积增大约1.44倍;当回灌水量相同时,溶质质量浓度增大2倍时,等Cl-浓度面积增大约0.92倍。[结论]回灌水溶质浓度和回灌水量对Cl-在地下水中的迁移均有一定的影响,而且回灌水量的影响大于溶质质量浓度的影响;增大回灌水量、减小回灌水溶质浓度利于Cl-的迁移扩散。     

基于化学动力学理论的中深层地下水资源评价——以四平市区为例

运用化学动力学和水动力学相结合的理论和方法,提取了反映中深层地下水的赋存环境特征、循环速度、资源量组成、可更新能力等方面的重要信息,并以此为依据进行了四平市区中深层地下水资源评价和补给能力分析。研究结果表明,目前四平市区该层地下水已经处于超采状态,四平市区中深层地下水具有补给能力较弱,补给资源有限,水循环滞缓的特点,作为供水水源缺乏保障性。     

地下水源热泵系统热平衡模拟三维数值模型

为了准确模拟预测地下水源热泵系统运行期间的热平衡变化规律特征,避免未来地下水源热泵系统运行期间出现的热贯通现象。以河北省水勘院正定基地地下水源热泵系统示范工程为例,建立了地下水渗流与热量运移三维耦合数值模型,并结合地下水源热泵系统的设计运行方案,预测分析了不同条件下未来地下水源热泵系统的热平衡发展趋势。结果表明,该示范工程按设计方案运行,抽、灌井之间存在热贯通现象。地下水源热泵系统通过增大温差的方法进行调节,可有效地缓解热贯通现象。     

Response of sediment biofilm to increased dissolved organic carbon supply in groundwater artificially recharged with stormwater

Purpose  

Best management practices encompass diverse artificial groundwater recharge (AGR) systems that heavily rely upon the capacity of the soil and vadose zone to retain large quantities of organic matter generated during stormwater runoff on urban catchments. However, the supply of stormwater-derived dissolved organic carbon (DOC) at the water-table region of aquifers can enhance the rate of biogeochemical processes by fueling heterotrophic microbial metabolism. This study examined changes in the abundance and activity of sediment biofilm in response to increased DOC supply at the water table of an urban aquifer intentionally recharged with stormwater. Changes in microbial abundance and activity under field conditions were compared with those measured in laboratory slow filtration columns supplied with an easily biodegradable source of DOC.     

Redistribution process of precipitation in ecological restoration activity of Pinus sylvestris var. mongolica in Mu Us Sandy Land,China

Precipitation is the most important water resource in semi-arid regions of China. The redistribution of precipitation among atmospheric water, soil water and groundwater are related to the land surface afforested ecological system. The study took widely replanted Pinus sylvestris var. Mongolica (PSM) in Mu Us Sandy Land (MUSL) as a research object and monitored precipitation, soil moisture, sap flow, and deep soil recharge (DSR) to find out moisture distribution in shallow soil layers. Results showed that the restoration process of PSM in MUSL changed the distribution of precipitation, with part of it infiltrating downward as DSR and part of it being stored in the shallow soil. Consequently, evapotranspiration increased and DSR significantly decreased, resulting in up to 466.9 mm of precipitation returning to the atmosphere through evapotranspiration in 2016. Vegetation increased soil water storage (SWS) capacity, with maximum SWS in PSM plot and bare sandy land (BSL) being 260 mm and 197 mm per unit horizontal area, respectively in 2016. DSR decreased from 54% of precipitation in the BSL plot to 0.2% of precipitation in the PSM plot in 2016. A great portion of infiltrated water was stored in the PSM ecosystem, resulting in a time lag of infiltration to reach the deep soil layer, and the infiltration rate in the BSL plot was 11 times of that in the PSM plot. SWS decreased 16 mm and 7.6 mm per unit horizontal area over a one-year period (from March to October, non-freezing time) in 2017 and 2019, respectively. The PSM annual sap flow was maintained at a relatively constant level of 154 mm/yr. Through in-situ measurement and comparative analysis of the precipitation redistribution of the BSL plot and the PSM plot, we find that PSM can significantly reduce the shallow soil water storage and DSR. However, substantial reduction of shallow soil water storage and DSR is detrimental for the long-term development of PSM forest. Therefore, it is necessary to reduce PSM density to cut the water consumption by PSM per unit area, thus to augment the shallow SWS and DSR, which will be beneficial for the PSM to survive under extreme drought conditions in the future. This study helps us understand the role of precipitation-induced groundwater recharge in the process of vegetation restoration in semi-arid regions and explains the possible causes of PSM forest degradation.     

Recommended urban storm water infiltration devices for different types of run-off under varying hydrogeological conditions

Background, aim, and scope  The decentralised near-natural infiltration of storm water in urban areas over a long-term period can cause local pollution of soil, seepage water and groundwater due to heavy metals (e.g. Pb, Zn, Cu), polycyclic aromatic hydrocarbons (PAH), petroleum hydrocarbons and readily soluble salts, which compounds are partly classified as hazardous. The aim of this paper is to present a recommendation matrix for suitable storm water infiltration devices. The scope is limited to eight different run-off types and two different infiltration devices (swales and trenches with three different trench-filling materials) under two different hydrogeological conditions (high adsorbing soil with low permeability, low adsorbing soil with high permeability). The examined run-off types are sub-divided as follows: run-off from unpaved areas (gardens, grassed areas, cultivated land); green roofs, aluminium roofs; roofs without zinc gutters and down-pipes; roofs with zinc gutters and down-pipes; copper roofs; zinc roofs and trafficked areas (cycle and pedestrian ways, yards, car parks and residential roads). The recommendation matrix should assist decision-makers such as city planners, architects and private house builders. Materials and methods  The potential for storm water infiltration to pollute soil, seepage water and groundwater is investigated with long-term 3-D numerical water flow and chemical transport modelling in unsaturated and saturated zones over 50 years, which were already presented by Zimmermann et al. (Water Sci Technol 51(2):11–19, 2005). The recommendation is based on a comparison between modelling results and several guideline values prepared by several German authorities. The evaluation process leads to four hazard levels regarding the impact on topsoil (i.e. first 20 cm of the soil), on seepage water (1 m below the infiltration device) and on groundwater (at the unsaturated–saturated boundary). Results  The recommendation matrix consists of 56 individual statements. Relating to dissolved organic substances like phenanthrene and fluoranthene, the infiltration of trafficked areas run-off is critical. The infiltration of metalliferous run-off has a high hazard accumulation potential. Here the storm water infiltration via sub-ground of low permeability and high adsorbing soil material is critical for seepage water in any case; the infiltration of zinc roofs run-off via trench infiltration devices is even critical for groundwater at 4 m depth. Sub-ground of low permeability and high adsorbing soil material has a lower potential hazard in terms of storm water infiltration from roof run-off. The storm water infiltration via swales effects a very large accumulation of heavy metals in the topsoil. The storm water infiltration via trenches leads to the accumulation of hazardous substances in the deeper sub-ground, particularly where the trench-filling material has low adsorbing capacity and high permeability. Discussion  The transferability of the results to other sites depends particularly on the hydrogeological conditions. Before using the recommendation matrix, details of the hydrogeological conditions should be collected. The long-term simulation process is simplified by several impact factors such as non-constant rainfall, soils heterogeneity, macro-porous flow, particle-bounded transport and microbiological decomposition. Conclusions  Based on the scale of risks to soils, seepage water and groundwater, the matrix should be used in the selection of the roof construction materials and appropriate storm water infiltration devices so that the environmental risks can be minimised. If the sub-ground has a high permeability and low adsorption capacities, the infiltration of metalliferous roof run-off water is, in general, not advisable without putting treatment facilities in place upstream. Thus, architects need to realise that the choice of a suitable infiltration device depends, on the one hand, on the type of run-off and, on the other hand, on the hydrogeological condition and the building materials. Recommendations and perspectives  Replacement of the topsoil in swale infiltration devices is recommended because, in particular, heavy metal (zinc) in run-off from roofs with zinc gutters and down-pipes accumulates in the soil matrix. The replacement interval depends on the hydrogeological conditions and, for this run-off example, lies between 10 and 20 years. If infiltration is essential, constructing special treatment facilities upstream can be an alternative. The existing numerical model could be adapted to suit other site-specific materials and be enhanced regarding several complex impact factors.     

Soil matric potential and salt transport in response to different irrigated lands and soil heterogeneity in the North China Plain

Purpose

In the lowland area of the North China Plain (NCP), increasing utilization of brackish water could promote the transformation of precipitation into available water resources, and alleviate the conflict between increase food production and freshwater scarcity. However, the processes of soil water movement and salt migration might be altered, because utilization of brackish water results in frequent changes in groundwater depth and thickness of vadose zone. Thus, it was necessary to understand soil water movement and salt migration when using brackish water for irrigation.

Materials and methods

In this study, soil matric potential (SMP) and total dissolved solids (TDS) at multiple depths were measured in situ to investigate the mechanisms of soil water movement and salt migration at one grassland (site 1) and at three typical irrigated croplands (sites 2, 3, and 4) with different soil textures and groundwater depths in a lowland area of the NCP.

Results and discussion

The study showed that deep soil water and groundwater were recharged generally following heavy precipitation during rainy season. SMP values increased quickly at site 4 due to relatively homogeneous soils, followed by site 3?>?site 2?>?site 1 with an obvious hysteresis response of SMP at multiple depths to precipitation. Soil water mainly moved downward in piston flow, and preferential flow also existed in the soil above 100 cm in the percolation process at four sites. Generally, SMP values followed the order of site 4?>?site 1?>?site 2?>?site 3 and exhibited an inverse trend for TDS, which was mainly due to soil heterogeneity and soil texture in vertical profiles. The differences in SMP among the four sites were mainly due to land use and groundwater depth. There were significantly differences in spatiotemporal distribution of water and salts between homogenous and heterogeneous soils. The processes of infiltration and water redistribution ended quickly in relatively homogeneous soils after heavy rains. However, there was obvious hysteresis in SMP with an increase in soil depth in heterogeneous soils.

Conclusions

Homogenous soils favored water infiltration, salt leaching, and groundwater recharge, and the flow of soil water flow was blocked and salt accumulated significantly in layered soils. The soil water movement and the transformation relationship between water and salt in the vadose zone provided a basis for utilization of brackish water irrigation in lowland region of the NCP.

     

Matrix and bypass-flow in quaternary and tertiary sediments of agricultural areas in south Germany

In hilly areas of south Germany with tertiary and quaternary sediments, percolation has been studied applying an isotope tracer of the water molecule in small-scale field experiments to better understand the hierarchies and interconnections of quick and slow seepage. On a catchment-related scale, these results have been connected with traditional and environmental isotope analysis of discharge to better quantify quick and slow seepage components, and to better assess the export of agrochemicals into ground- and surface waters. Consequently, the development of improved application techniques of agrochemicals and better strategies for ground and surface water protection is possible. The unsaturated zone of the study area was traced with Deuterium on areas of about 50 m². Results show that infiltration splits into bypass and matrix-flow. Bypass-flow exceeds flow velocities of 0.5 m day⁻¹, which is close to flow velocities of overland-flow, and matrix-flow ranges between 0.7 m year⁻¹ (Loess) and 1.2 m year⁻¹ (Tertiary gravels and sands). In these unconsolidated rocks, bypass-flow seems to (1) be strongest under wet and dry conditions at the soil surface; (2) be more dominant in coarse than fine-grained sediments; (3) be more pronounced in terrestrial than in marine sediments; and (4) penetrate to an average depth of less than 1 m in fine-grained sands and silts, and deeper than 3 m in gravels before it either finally incorporates into matrix-flow or generates interflow. Hydrographic analysis shows that more than 21% infiltration produces interflow by the transformation of bypass-flow into lateral flow, and about 75% infiltration groundwater recharge; 4% of bypass-flow incorporates into matrix-flow. In the study area, plowing techniques and field size influence significantly and proportionally the distribution of overland- and interflow-flow. However, groundwater recharge is not significantly changed. As matrix-flow is too slow an indicator to clarify how changes in land use affect groundwater quality over time, the analysis of direct discharge may be considered a good early indicator to assess land use changes on the export of agrochemicals.